For many uses, it is desirable to have available an aircraft which can take-off from a very small surface and which therefore does not require a specific large airport for example. Furthermore, for particular purposes of use, an aircraft is required which is agile, which can be maneuvered precisely and which can preferably hover on the spot and, in this respect, can have good hover flight characteristics.
For example, aircraft are used for aerial surveillance and aerial reconnaissance, which aircraft hover above an object of interest and while so doing are able to record aerial images, for example. In an alternative use, an aircraft capable of vertical take-off, sometimes also called VTOL (vertical take-off and landing), can be used to approach territories which cannot be easily accessed by people or miscellaneous machines, for example as part of a disaster management intervention, to be able to transport goods, such as tools, food or medicines, into such territories.
Aircraft have been developed for such uses, inter alia, in which at least three, preferably four or more rotors fitted with a propeller and a motor driving said propeller respectively provide a substantially vertically upwardly directed thrust to thereby allow the aircraft to be able to take off vertically or to hover. An aircraft provided with four rotors of this type is also known as a quadcopter, quadrocopter, quadricopter, quadrotor or hover platform. Aircraft of this type having more than three thrust-providing rotors are generally known as multicopters and, in addition to quadcopters, variants with three rotors (tricopters), six rotors (hexacopters) or eight rotors (octocopters) are also common. Aircraft of this type are generally operated unmanned and thus can be small. These aircraft are sometimes also called drones.
By slightly inclining the entire aircraft or one or more rotors out of the horizontal, it is possible in aircraft of this type to also provide a particular propulsion in which a thrust generated by the rotors is inclined out of the vertical. However, cruising speeds which are achievable in this manner are restricted to relatively low speeds of typically less than 200 km/h, often even less than 100 km/h, due to physical boundary conditions which arise in this type of aircraft. A speed restriction of this type results, for example from the physical boundary condition that the propellers used for lift are operated at high rotational speeds, and therefore a propeller blade moving forwards in the direction of flight of the aircraft must move almost at sonic speed at least at the tips of the propeller blade even at relatively low cruising speeds, as a result of which a high air resistance and a loud noise are generated.
Therefore, although conventional multicopters have good hover characteristics like helicopters in which only a single rotor provides the necessary lift and complicated rotor mechanics can be used together with a tail rotor for maneuvering the helicopter, they usually only achieve relatively low cruising speeds.
KR 10 2012 006 05 90 A discloses a quadrocopter which can take off and land vertically and in which a thrust direction can be varied by propellers to be able to provide not only lift, but also propulsion for the quadrocopter.